1. Field of the Invention
The invention relates to a D/A converter, and in particular to a D/A converter with a Gamma correction circuit.
2. Description of Related Art
Generally, in a conventional digital-to-analog converter (DAC), an output voltage is required to have a linear relation with the input digital data. However, in certain special cases, an output voltage of the DAC must have a non-linear relation with the input digital data. For example, in liquid-crystal display (LCD) applications, the relation between the brightness and voltage of an LCD is not linear. Therefore, a correction circuit generally called a Gamma correction circuit is utilized for compensation.
FIG. 1 shows the structure of a R-DAC with a Gamma correction circuit according to the prior art. In this conventional R-DAC, digital data D0.about.D5 are decoded by the use of a ROM decoder, and then a voltage-dividing resistor is selected from a reference voltage generator 2 to output a corresponding voltage. The above-mentioned approach is simple, but taking an LCD application as an example, the number of gray levels varies directly with the space occupied by its structure. For example, the area of the R-DAC with 256 gray levels is 5.3 times that of the R-DAC with 64 gray levels. Therefore, in the LCD application, the DAC occupies most of the area of a data driver.
FIG. 2 is a circuit diagram of a 2-divided C-DAC with a Gamma correction circuit. Even though the area of the 2-divided C-DAC is smaller than that of the R-DAC, many capacitors which take up a large area are used. Therefore, the area of the 2-divided C-DAC can be further reduced.